Semiconductor lasers are used in many different applications, such as in optical fiber communications, where they can be used at the interface between the electronic signal processing circuitry and the optical transmission lines. The semiconductor laser device generates light that is transmitted through the optical fiber. For this purpose, a semiconductor laser package or module includes the semiconductor laser device and a portion of the optical fiber, as well as other optical components, including at least one lens and at least one isolator. These components are held at fixed positions within the module so as to assure that the light generated by the laser device is effectively coupled into the optical fiber at an end of the optical fiber. The process of aligning an optical fiber to a laser device and fixing it in place is sometimes referred to as fiber pigtailing. Currently in the industry, there are two types of form factors for laser packages or modules. One is the coaxial or TO (transistor outline) package and the other is the flat pack. The flat pack form factor package includes arrangements such as butterfly packages, mini-tail packages, mini-dil packages, etc.).
Flat form factor laser modules basically comprise a set of components, including a semiconductor laser device, a lens, and isolator and a fiber sleeve holding an optical fiber. These components can be mounted on some kind of support or optical bench which is housed inside a box-like hermetically sealed housing, and the laser device (such as the laser diode) and its related circuitry, sometimes referred to as a laser block, are electrically connected to one or more pins, which can extend laterally from the housing (such as in the so-called butterfly laser modules).
FIG. 1 shows one possible configuration of some of the above-mentioned elements: a laser block 11 (including a semiconductor laser device 1 such as a laser diode, having a light-emitting surface or end), an optical lens 2 arranged in a lens holder 21, an isolator 3A arranged in an isolator holder 3B, and an optical fiber sleeve 4 (also known in the art as a ferrule, basically made up of a rigid tube) arranged in a sleeve holder 4A, are all arranged on an L-shaped support. The lens 2 is arranged for focusing the light emitted by the laser device onto an end of an optical fiber (not shown in FIG. 1) and the isolator is arranged to prevent light from being reflected back towards the laser device from the optical fiber end and the surrounding parts of the assembly. Suitable lenses, isolators and fiber sleeves (or ferrules) are well known in the art and there is no need to further describe these elements here.
In the semiconductor laser module, the assembly illustrated in FIG. 1 can be placed on a cooling device, such as a thermo-electric cooler (TEC) or Peltier effect element, which can be used to control the temperature of the laser device the permit higher performance and/or operation over a greater power range.